Some vehicle engines utilize cylinder deactivation technology, which deactivates one or more engine cylinders at lower engine speeds to provide desired engine performance and to optimize fuel economy, for example. Exhaust valve assemblies have been used in vehicle exhaust systems to attenuate exhaust noise in exhaust systems using cylinder deactivation technology.
One type of exhaust valve that has been used is a spring loaded passive valve, which does not specifically respond to cylinder deactivation demands, but instead only operates depending upon exhaust flow rate. This type of “passive” valve is resiliently biased toward a closed position, and moves to an open position when exhaust flow rate is sufficient to overcome this biasing force. Thus, the exhaust valve is closed at idle and low engine speeds in full cylinder mode, which may be undesirable in terms of engine performance and sound characteristics.
Another type of exhaust valve that has been used is an “active” exhaust valve. An electric actuator is used to actively control the exhaust valve to move the exhaust valve between closed and open positions. One advantage of an electrically controlled valve is that full valve opening can be facilitated without requiring an added backpressure element. Passive valves typically have to include an element to add backpressure such that the valve can be held in a desired open position under high flow conditions. A disadvantage with active valves is that there is additional expense resulting from a need for diagnostics to sense error states.
An additional disadvantage is that an active valve will normally remain in a fixed position regardless of flow. In some applications this can generate a higher backpressure than desirable in the closed position at a higher end of a “closed valve” flow condition.
Thus, there is a need for a cost effective solution for exhaust valve control that can be used with cylinder deactivation technology to provide desired performance and sound characteristics.